Error: Number of records with member ID that were skipped to prevent problems with other custom data sync - when viewing a Custom Constituent Import result page

I am trying to do a Custom Constituent Import, but I consistently get this error in the results page, e.g.:

Number of constituents records created: 17Number of constituent records updated: 1Number of interest opt-in assignments: 0Number of interest opt-out assignments: 0Number of group assignments added: 111Number of group assignments removed: 0Number of center assignments added: 0Number of center assignments removed: 0Number of record opted into a center: 0Number of record opted out of a center: 0Number of records with member ID that were skipped to prevent problems with other custom data synch: 94Number of uploaded records with errors that were rejected: 11

Article
Number:68892

Products:

Luminate_Online

This happens because you have a connector or a custom sync. When your site is configured with a connector or a custom sync, your site is also configured to not allow certain kinds of one off uploads to maintain data integrity. This includes:

Creating a new record via an upload with a member ID where the member ID is not already in Luminate Online - If you need to upload new records with a member ID, create the record in your offline database and allow your sync/connector to add the record to Luminate Online.

Updating an existing record that already has a member ID - If you need to updating an existing record that already has a member ID, update that record in your offline database and allow your sync/connector to update the record in Luminate Online.